I've had this problem come from out of no where, about a year ago. Tried all kinds of antiperspirants, even Certain dry didn't work that well (plus it was harsh on my skin)
So what I did was switch from Antiperspirant to deadorant. Sounds stupid but it worked - I also trimmed the hair, this helps a lot.
it takes awhile for your body to adjust to the deodorant ( ~ week ) ... but it's been a solid year of no sweaty pits, all from just the switch.
at some point I'll have to switch back to an antiperspirant I'm sure, but it will be more effective when I do.
theres plenty of info out there about this - you basically just cycle antiperspirant with plain deodorant once one or the other becomes ineffective.
worked for me. Good luck, I know the sweaty pits are a bummer.